Companies aim higher for wind-turbine energy

BOSTON - The world's strongest winds race high in the sky, but that doesn't mean they're out of reach as a potentially potent energy source.

BOSTON - The world's strongest winds race high in the sky, but that doesn't mean they're out of reach as a potentially potent energy source.

Flying, swooping and floating turbines are being developed to turn high-altitude winds into electricity.

The challenges are huge, but the potential is immense. Scientists estimate the energy in the jet streams is 100 times the amount of power used worldwide annually.

Cristina Archer, an atmospheric scientist at California State University in Chico, said there's "not a doubt anymore" that high-altitude winds will be tapped for power.

"This can be done. It can work," she said.

The question is, when? Some companies project their technology will hit the market in several years, but Fort Felker at the National Renewable Energy Laboratory says the industry is 10 years from making a meaningful contribution to the nation's electricity demands.

No company, for example, has met the basic requirement of demonstrating that its turbine can fly unsupervised safely for prolonged periods of time.

High-altitude wind power is similar to ground wind in the 1970s - facing questions, but soon to prove its viability, said PJ Shepard of Oroville, Calif.-based Sky WindPower, which is developing a "flying electric generator."

"It's kind of like the adjustment folks had to make when the Wright brothers started flying airplanes," she said.

The lure of high-altitude wind is simple: Wind speed generally increases as surface friction diminishes. Each time wind speed doubles, the amount of energy it theoretically holds multiplies by eight.

The world's most-powerful winds circulate in the jet streams, which are found 4 miles to 10 miles off the ground and carry winds that regularly break 100 mph.

The dream is to tap the jet streams, but for now, high-altitude wind companies are focusing on below a 2,000-foot ceiling, above which complex federal air-space restrictions kick in. Adam Rein, co-founder of the Boston company Altaeros Energies, said his company calculates winds at the 2,000-foot level. Winds at that level are up to 21/2 times as strong as winds that can be reached by a typical 350-foot land turbine.

High-altitude wind advocates say their smaller, lightweight turbines will be far cheaper to build and deploy than windmills with huge blades and towers that must be drilled into land or the sea floor.

Those savings would mean inexpensive energy, as low 2cents per kilowatt hour.

Advocates say there are plenty of remote and offshore no-fly areas where they won't interfere with aircraft and have minimal interaction with people.

Felker said keeping the turbines operating autonomously over long periods in changing weather might be the biggest obstacle.